The invention concerns a device for obtaining one after another and from at least two spatially separated areas the components of a liquid, especially stabilized whole blood contained in a flexible bag with at least one line leading out of it.
In the devices that have been available up to now for separately obtaining the components of a liquid, especially whole blood in centrifuged bags, the bag containing the liquid or whole blood is squeezed between a perpendicular and stationary plate and another plate that is hinged to the bottom of the first and can be pivoted toward it.
The requisite force is obtained with springs. These devices, conventional plasma squeezers, have considerable drawbacks, however. First, the squeezing procedure must be constantly monitored and decelerated or terminated once a particular layer of components has been attained at the upper edge. Second, since the force of the springs decreases while the bag is being squeezed, greater force than can be obtained from the springs alone must be exerted to squeeze a more viscous layer, the Buffy-coat layer for instance, out of the blood. Layers of that type can usually be obtained only by adding manual force. Finally, only bags with an outlet at the top can be employed in these devices.
The conventional plasma squeezers have been improved by the addition of a cell sensor, making it unnecessary to monitor the squeezing procedure. The inhomogeneities in pressure due to the use of springs, however, are still present along with the associated drawbacks.
A considerable improvement in the aforesaid devices has been attained with automatic drive mechanisms.
German OS 3 012 228 describes a device wherein the pressure is applied hydraulically, pneumatically, or hydropneumatically. Sensors for determining the various component layers allow automatic squeezing.
German OS 3 417 892 also describes an automatic device wherein the squeezing structure is accommodate between an upper and a lower pressure-application plate, requiring three separately operated pressure-application structures.
The stationary plate and the moving plate are parallel in both devices, and the bag must accordingly be manually secured between the plates until the squeezing procedure is initiated and it can be secured by the commencing pressure. Since the bag is teardrop-shaped, however, it will rapidly deform and create turbulence in the interface between its contents, making it more complicated to squeeze out a pure layer of component. Since the force exerted on the stationary plate is relatively high (approximately 50 kp), the plates must be relatively strong.